UTC L1937 LINEAR INTEGRATED CIRCUIT WHITE LED STEP-UP CONVERTER 2 1 3 DESCRIPTION The UTC L1937 is a step-up DC/DC converter specifically designed to drive white LEDs with a constant current. The device can drive two, three or four LEDs in series from a Li-Ion cell. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors. The UTC LT1937 switches at 1.2MHz, allowing the use of tiny external components. The output capacitor can be as small as 0.22 μF, saving space and cost versus alternative solutions. A low 95mV feedback voltage minimizes power loss in the current setting resistor for better efficiency. 5 4 SOT-25 1 SOT-363 FEATURES * Inherently Matched LED Current * High Efficiency: 84% Typical * Drives Up to Four LEDs from a 3.2V Supply * Drives Up to Six LEDs from a 5V Supply * 36V Rugged Bipolar Switch * Fast 1.2MHz Switching Frequency * Uses Tiny 1mm Tall Inductors * Requires Only 0.22μF Output Capacitor *Pb-free plating product number: L1937L APPLICATIONS * Marking code: LTCG * Cellular Phones * PDAs, Handheld Computers * Digital Cameras * MP3 Players * GPS Receivers PIN FUNCTION PIN NO. PIN NO. PIN NAME (SOT-25) (SOT-363). 5 SYMBOL 1 Switch SW 2 Ground GND 3 Feedback FB 4 Shutdown 6 5 UTC Input Supply Ground SHDN VIN GND FUNCTION Connect inductor/diode here. Minimize trace area at this pin to reduce EMI. Connect directly to local ground plane. Reference voltage is 95mV. Connect cathode of lowest LED and resistor here. Calculate resistor value according to the formula: RFB = 95mV/ILED Connect to 1.5V or higher to enable device;0.4V or less to disable device. Input Supply Pin. Must be locally bypassed. Connect to Pin 2 and to local ground plane UNISONIC TECHNOLOGIES CO., LTD. 1 QW-R103-021,A UTC L1937 LINEAR INTEGRATED CIRCUIT BLOCK DIAGRAM ( PIN 6 FOR SOT-363 PACKAGE ) VIN FB SW 5 3 1 COMPARATOR 95mV VREF 1.25V A1 + A2 + Rc Cc S Q Q1 + Σ 0.2Ω - RAMP GENERATOR SHDN 4 DRIVER R SHUTDOWN GND 2 1.2MHz OSCILIATOR ( PINS 2 AND 5 FOR SOT-363 PACKAGE ) ABSOLUTE MAXIMUM RATINGS PARAMETER Input Voltage SW Voltage FB Voltage SHDN Voltage Operating Temperature Storage Temperature Maximum Junction Temperature Lead Temperature (Soldering, 10 sec) SYMBOL RATINGS UNIT VIN VSW VFB VSHDN Topr Tstg Tj TLead 10 36 10 10 -40 ~ +85 -65 ~ +150 125 300 V V V V ℃ ℃ ℃ ℃ ELECTRICAL CHARACTERISTICS (Ta=25℃, VIN=3V, VSHDN=3V, unless otherwise noted.) PARAMETER SYMBOL Operating Voltage Feedback Voltage FB Pin Bias Current Supply Current VIN VFB IFB Switching Frequency Maximum Duty Cycle Switch Current Limit Switch VCESAT Switch Leakage Current SHDN Voltage High SHDN Voltage Low SHDN Pin Bias Current fosc DC ISW UTC Icc TEST CONDITIONS ISW =100mA,Duty Cycle=66% MIN 86 10 SHDN=0V VCESAT(SW) ISW =250mA ISW(OFF) VSW =5V VIH VIL ISHDN 0.8 85 TYP MAX UNIT 95 45 1.9 0.1 1.2 90 320 350 0.01 10 104 100 2.5 1.0 1.6 5 1.5 0.4 65 UNISONIC TECHNOLOGIES CO., LTD. V mV nA mA µA MHz % mA mV µA V V µA 2 QW-R103-021,A UTC L1937 LINEAR INTEGRATED CIRCUIT TYPICAL APPLICATIONS Conversion Efficiency 90 L1 22μF D1 C1 1μF VIN SW LED 2 15mA LED 3 OFF ON SHDN 85 C2 0.22μF LED 1 EFFICIENCY(%) VIN 3V ~ 5V FB R1 6.34Ω GND 80 VIN=3V VIN=3.6V 75 70 65 Li-Ion Powered Driver for Three White LEDs 60 0 5 15 10 20 LED CURRENT (mA) Two LED Efficiency 86 L 22μH CIN 1μF SW 90k 5k SHDN FB GND 82 COUT 1μF VDC DIMMING VIN VIN=3.6V 84 D R1 2Ω VIN=3V EFFICIENCY(%) VIN 3V ~ 5V 80 78 76 74 72 Li-Ion to Two White LEDs 70 0 10 20 30 40 LED CURRENT (mA) UTC UNISONIC TECHNOLOGIES CO., LTD. 3 QW-R103-021,A UTC L1937 LINEAR INTEGRATED CIRCUIT Three LED Efficiency 90 L 22μH D CIN 1μF 85 COUT 0.22μF VDC DIMMING VIN EFFICIENCY(%) VIN 3V ~ 5V SW 90k 5k UTC LT1937 SHDN FB R1 4Ω GND 80 VIN=3V VIN=3.6V 75 70 65 Li-Ion to Three White LEDs 60 15 10 5 0 20 LED CURRENT (mA) Five LED Efficiency 85 L 22μH CIN 1μF COUT 0.22μF VDC DIMMING VIN SW 90k 5k SHDN FB GND R1 4Ω 80 EFFICIENCY(%) VIN 3V ~ 5V D VIN=3V 75 VIN=3.6V 70 Li-Ion to Five White LEDs 65 0 2 4 6 8 10 12 LOAD CURRENT (mA) UTC UNISONIC TECHNOLOGIES CO., LTD. 4 QW-R103-021,A UTC L1937 LINEAR INTEGRATED CIRCUIT Seven LED Efficiency 85 L 22μH VIN 5V D CIN 1μF EFFICIENCY(%) VIN SW 90k SHDN 5k FB 80 COUT 0.22μF VDC DIMMING R1 4Ω GND 75 70 65 5V to Seven White LEDs 0 5 10 15 LOAD CURRENT (mA) Four LED Efficiency 85 L 22μH D CIN 1μF COUT 0.22μF VDC DIMMING VIN SW SHDN FB 90k 5k GND R1 4Ω 80 EFFICIENCY(%) VIN 3V ~ 5V VIN=3V VIN=3.6V 75 70 Li-Ion to Four White LEDs 65 0 5 10 15 20 LOAD CURRENT (mA) UTC UNISONIC TECHNOLOGIES CO., LTD. 5 QW-R103-021,A UTC L1937 LINEAR INTEGRATED CIRCUIT TYPICAL PERFORMANCE CHARACTERISTICS Quiescent Current 2.2 SHDN Pin Bias Current 400 -50℃ 2.0 350 100℃ 25℃ 1.6 SHDN PIN BIAS CURRENT (μA) 1.8 IQ (mA) 1.4 1.2 1.0 0.8 0.6 0.4 300 SHDN=10V 250 200 150 SHDN=3.6V 50 0.2 SHDN=2.7V 0 2 0 4 6 8 0 -50 10 -25 VIN (V) 0 25 50 75 100 75 100 TEMPERATURE (℃) Switching Frequency Feedback Bias Current 1.4 60 1.2 50 FEEDBACK CURRENT (nA) SWITCHING FREQUENCY (MHz) SHDN=3V 100 1.0 0.8 0.6 0.4 40 30 20 10 0.2 0 -50 -25 0 25 50 75 0 -50 100 -25 TEMPERATURE (℃) 0 25 50 TEMPERATURE (℃) Efficiency vs Temperature Current Limit vs Duty Cycle 350 85 VIN=3.6V 3 LEDs 300 ILED =20mA CURRENT LIMIT (mA) Efficiency(%) 84 ILED=15mA 83 ILED=10mA 82 250 200 150 100 81 50 80 -50 0 0 50 TEMPERATURE (℃) UTC 100 0 20 40 60 80 100 DUTY CYCLE (%) UNISONIC TECHNOLOGIES CO., LTD. 6 QW-R103-021,A UTC L1937 LINEAR INTEGRATED CIRCUIT UTC assumes no responsibility for equipment failures that result from using products at values that exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or other parameters) listed in products specifications of any and all UTC products described or contained herein. UTC products are not designed for use in life support appliances, devices or systems where malfunction of these products can be reasonably expected to result in personal injury. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. UTC UNISONIC TECHNOLOGIES CO., LTD. 7 QW-R103-021,A